Floating escapement mechanism



April 10, 1956 R. D. DODGE 2,

FLOATING ESCAPEMENT MECHANISM Filed June 4. 1953 2 Sheets-Sheet l u k 6 27 9m INIENTOR.

RONALD D. DODGE ATTORNEY April 10, 1956 R. D. DODGE FLOATING ESCAPEMENT MECHANISM 2 Sheets-Sheet 2 Filed June 4. 1955 FIG. 2

INVENTOR.

RONALD D. DODGE JTTORNEY United States Patent C) FLOATING ESCAPEMENT MECHANISM Ronald D. Dodge, Poughkeepsie, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application June 4, 1953, Serial No. 359,598

1 Claim. (Cl. 19786) This invention relates to a typewriter carriage spacing mechanism, and more particularly to a floating escapement mechanism for a typewriter carriage.

In conventional typewriter construction, a carriage by definition, is a device for holding a work sheet, and for moving the same in steps into a printing position. A carriage is a heavy mass high inertia element since it usually comprises a pair of rails slidable in a suitable track mounted on the typewriter base; a platen; line spacing mechanism; paper bail; and a toothed rack. The rack which is secured to the carriage, has teeth which are pitched in accordance with the class of type used by the machine, e. g., for pica type, the rack teeth are spaced .100" apart. An escapement pawl is mounted on the typewriter base in operative engagement with the carriage rack to control the stepped movement of a spring biased carriage into alignment with the machines single print position.

In a usual construction, the escapement pawl is operated by a type bar; i. e., any type bar, during a print stroke, and before it actually prints, strikes a universal bar which actuates the escapement pawl to release the spring biased carriage for movement one step at a time. Such a general construction is shown in U. S. Patent 1,945,847, C. W. Crumrine.

The normal carriage escapement mechanism briefly outlined above, has worked satisfactorily for years at typewriter speeds in the order of 25 character strokes per second or less; but above that print rate the escapement mechanism does not operate effectively, and there is a tendency for the machine to overprint characters.

It is an object of this invention, therefore, to provide an improved typewriter carriage spacing control mechamsm.

It is a further object of this invention to provide an improved typewriter carriage construction having a light mass spacing control rack mounted for limited slideable movement relative to the heavy carriage base.

Other objects of the invention will be pointed out in the following description and claim and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

Briefly, this invention relates to an improved carriage construction wherein a light mass carriage rack is positioned for controlled slideable movement relative to the carriage proper, and wherein the light mass rack can be moved into a position for an escapement action, before the heavy mass carriage reaches a corresponding position.

In the drawings:

Fig. 1 is a perspective exploded view of a portion of a typewriter construction utilizing the improved spacing control rack, while Figs. 2 and 3 are partial plan views of the carriage and rack construction shown in Fig. 1.

Referring to the drawings and particularly to Figs. 1 and 2, a carriage escapement mechanism 1 is shown comprising a carriage base 2, a rack 3, an escapement pawl 4,

life

an escapement trip lever 5, and an actuating means such as type bar 6.

Actually, the carriage base 2 supports a work sheet holding platen 7, and associated line spacing and tabulating mechanisms (not shown). Accordingly, the carriage should be considered as a heavy mass element which, because of its high inertia, is slow to start moving. The base 2 is mounted for stepped transverse movement in response to a pull exerted by a tensioned tape 8, which pulls the carriage to the left (Fig. 1), across the typewriter print position 9. The tension in tape 8 is small in comparison to the mass of the carriage base 2, and, therefore, the carriage base starts moving slowly, but it is constantly accelerated by the tape into the next print position.

The rack 3 (Figs. 2 and 3) is provided with a plurality of teeth 10, having a line pitch determined by the particular size of the type to be used (e. g., .100" for pica type). Each tooth has a suitable blocking or stop surface 11 for engagement with pawl 4 thereby determining the limits of a stepped rack movement hereinafter described. Each rack tooth further has a crown 12 over which the nose 13 of the pawl must be lifted to be brought into engagement with a sloping or spacing surface 14 of a rack tooth.

The escapement pawl 4 further has a tail 15 which is positioned for actuation by the escapement trip lever 5 to pivot the nose 13 out of engagement with any tooth stop surface 11. Specifically, pawl 4 is mounted for both pivotal and slideable movement with respect to the typewriter base by providing it with an elongated aperture 16 engageable with a stud 17 secured to the typewriter base. Further, when pawl 4 is pivoted by the escapement trip lever 5, a spring 18, interconnecting pawl 4 and the typewriter base, pulls pawl 4 over the crest 12 of a tooth 10 and into sliding engagement with a spacing surface 14 (to the position shown in Fig. 3). Spring 18 also biases pawl 4 clockwise about pivot 17 and into engagement with the rack teeth.

Trip lever 5 is mounted for pivotal movement in a vertical plane, and since its operation is explained in detail in U. S. Patent 1,945,847, C. W. Crumrine, it is felt that a short summary statement of operation should be sulficient at this time. Specifically, trip lever 5 (Fig. 1) is mounted on a stud 19 secured to the typewriter base. The tail of lever 5 is connected by link 20 to a universal bar 21 which, in turn, is mounted for oscillating movement in response to impact from a type bar enroute to the print position 9, i. e., the universal bar is spring biased (not shown) to a rest position (not shown), and it is driven by a type bar from the rest position to an actuating position (Fig. 1) wherein it is just about to pivot pawl 4 out of engagement with rack teeth 10.

Actually, a plate 22 is positioned between pawl 4 and the nose 23 of the actuating lever 5. Plate 22, which is parallel to pawl 4, has an elongated aperture 24 (Fig. 2) by which it is mounted on pin 17 under pawl 4. Plate 22 is biased by spring 25 to the right into the normal position shown in Fig. 2. Plate 22 further has a shoulder 26 that overlies the tail 15 of pawl 4 when it is in the rest position shown in Fig. 1, and which is struck by nose 23 of actuating lever 5 to effect the tripping of pawl 4 from the position shown in Fig. 2. The stroke of the pawl is not long enough to abut against the lever 5. If the tripping lever is actuated while the pawl is moving into its tripping position and the lever 22 were held forward during the leftward movement of the pawl, the latter would abut the vertical extension 26 and consequently, lever 22 is provided with a slot 24 and spring 25 so that it may yield and not present a positive block to the pawl. If thereafter, the lever 5 is released, the lever 22 would then under influence of spring 25, snap back to the position of Fig. 2 lever 15:

The operation of type bar 6 is also well known, but basically (see Fig. 1) it is rotatably supported in a segment 27 which guides the movement of the type bar from rest to a printing position. A type bar actuating lever 28 is conditioned for actuation by key bar 29 and it is driven by power roll 30 to exert a pull on link 31 and thus rotate the type bar 6 to printing position 9 (Fig. 1). This type bar action is shown in detail in U. S. Patent 2,506,444 assigned to same assignee as that of the present invention.

In the disclosed embodiment, rack 3 is mounted for controlled slideable movement relative to carriage base 2. Specifically, the carriage base 2 is provided with a plurality of outstanding pins 32 (Figs. 2 and 3) while the rack 3 defines suitable elongated apertures 33. The pins are passed through the apertures and peened over or otherwise suitably prevented from slipping through the apertures. Actually, the apertures 33 have a transverse diameter slightly greater (sliding fit) than that of the pins 32, but in an axial direction, the apertures are elongated to permit the desired relative axial movement between the rack and carriage base. A spring 34 (Figs. 2 and 3) is then tensioned between a bracket 35 on the carriage base 2 and a pin 36 secured to the rack 3 and extending through a slot 36a in the carriage base. With this structure, the rack normally is biased to the left (Fig. 3) so that the ends 37 of the apertures 33 are brought into contact with the pins 32 when pawl nose 13 is not in engagement with a stop surface 11 of a rack tooth (see Fig. 3). That is, when the pawl nose 13 is released from a rack tooth, spring 34 tensions the light mass rack 3 and pulls it very rapidly to the left until the end 37 of the aperture is in contact with the pin 32. Then as the slower moving carriage base 2 is pulled to the left by tape 8, the stop surface 11 of a rack tooth engages the nose 13 of pawl 4 and pushes the pawl towards its rest position (Fig. 1), wherein the tail 15 registers with shoulder 26. Pawl 4 is thus stopped by the right end of aperture 16 hitting pin 17. This also stops the rack since the nose 13 of pawl 4 is in engagement with a tooth stop surface 11. Then, because of the floating rack mounting, the carriage base continues to move against the tension of spring 34 and until pins 32 engage the left end peripheral wall 38 of apertures 33 (Fig. 2).

This construction not only quiets the carriage stepped movement-through the cushion provided by spring 34 but further it permits the escapement rack to drive pawl 4 into tripping position before the heavy carriage base has moved into printing position.

wherein its ledge would get behind the Tests made on a typewriter having this improved floating rack construction show that the escapement mechanism functions properly at type bar stroke rates ranging from 15% to 30% faster than could be used with conventional carriage construction wherein the rack is rigidly secured to the carriage base.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claim.

What is claimed is:

An escapement mechanism for a carriage of a business machine comprising, in combination, a printing mechanism, a carriage base, means biasing said carriage base for movement in one direction across a fixed printing position, a toothed rack having a tooth pitch equal to the desired stepped movement of said carriage, means mounting said rack on said carriage base for controlled relative axial movement therebetween, means biasing said rack for movement in said one direction relative to said carriage base, a pawl mounted on said machine for releasable engagement with said rack thereby to limit the movement thereof, means supporting said pawl for both pivotal and limited longitudinal movement relative to said carriage, biasing means acting on said pawl for urging the latter into engagement with said rack and toward one limit of its longitudinal movement in a direction opposite to that produced on said rack by said rack biasing means, and means responsive to operation of said printing means when said pawl is moved to the other limit of its longitudinal travel for releasing said pawl from one tooth of said rack whereby said pawl and rack are free for movement each in response to its respective biasing means and in opposite directions so that said pawl engages the next tooth on said rack before the carriage base has moved through the desired pitch distance.

References Cited in the file of this patent UNITED STATES PATENTS 430,775 Hamilton June 24, 1890 585,235 Sears June 29, 1897 633,139 Killman et al Sept. 19, 1899 1,539,009 Barney May 26, 1925 

